The three-dimensional structures of aldolase from rabbit muscle and of glutamine synthetase from E. coli are being investigated by x-ray crystallographic methods. Cable-like aggregates of glutamine synthetase that form in the presence of divalent cations are being studied by electron microscopy and image processing methods. The subunit arrangement in ribulose diphosphate carboxylase from tobacco is being investigated by combined x-ray diffraction and electron microscopy. BIBLIOGRAPHIC REFERENCES: T.G. Frey, D. Eisenberg, and F.A. Eiserling, "Glutamine Synthetase forms Three and Seven-Stranded Cables," Proc. Nat. Acad. Sci., 72, 3402-3406 (1975). W.J. Scanlon and D. Eisenberg, "Solvation of Crystalline Proteins," J. Mol. Biol., 98, 485-502 (1975).